A rule-based query language for HTML

With the recent popularity of the Web, an enormous amount of information is now available online. Most Web documents available over the Web are in HTML format and are hierarchically structured in nature. How to query such Web documents based on their internal hierarchical structure becomes more and more important. We present a rule-based language called WebQL to support effective and flexible Web queries. Unlike other Web query languages, WebQL is a high level declarative query language with a logical semantics. It allows us to query Web documents based on their internal hierarchical structures. It supports not only negation and recursion, but also query result restructuring in a natural way. We also describe the implementation of the system that supports the WebQL query language.